Pt Electrocatalyst Supported on a 3D-Nanoporous Carbon Shows a High Performance in a High-Temperature Polymer Electrolyte Fuel Cell

Considerable attention has been focused on the high-temperature PEFCs (> 100 ^oC), due to their benefiting PEFCs with higher carbon monoxide (CO) tolerance, faster electrochemical kinetics, and better water management than those of conventional PEFCs. However, the high-temperature PEFCs also suffer from their low durability in terms of carbon corrosion and platinum nanoparticles (Pt-NPs) aggregation resulting in the detachment of the Pt-NPs from the catalysts and loss in electrochemical surface area (ECSA) as well as the degradation of FC performance. Thus, enhancement in durability is highly demanded for the commercialization of the next-generation PEFCs.

    We have already reported that poly[2,2’-(2,6-pyridine)-5,5’-bibenzimidazole] (PyPBI) is an efficient dispersant for carbon supporting materials and provides the anchor sites for the Pt-nanoparticles (NPs) as well as creating the so-called three-phase boundary structure[1-7].

    In this paper, we used a 3D nanoporous carbon (NanoPC) with a high specific surface area of 1,037 m²/g as a carbon support for high-temperature polymer electrolyte fuel cell, and fabricated an electrocatalyst (NanoPC/PyPBI/Pt) having platinum nanoparticles of ca. ~2.2 nm diameter deposited on the NanoPC that was wrapped by poly[2,2’-(2,6-pyridine)-5,5’-bibenzimidazole] (PyPBI). Even after 10,000 start-up/shutdown cycles in the range of 1.0 to 1.5 V vs. RHE, the NanoPC/PyPBI/Pt showed almost no loss in electrochemical surface area (ECSA), which was much higher durability than those of a CB/PyPBI/Pt (~32%-loss), in which conventional CB was used in place of the NanoPC, and conventional CB/Pt (~46%-loss).

    FC performance of the assembled MEAs was evaluated at 120 ºC without any external humidification using a computer-controlled fuel cell test system. The polarization and the power density curves were measured under the atmospheric pressure by flowing dry hydrogen (flow rate; 100 mL/min) and dry air (flow rate; 200 mL/min) at the anode and the cathode, respectively.

    The power density of the NanoPC/PyPBI/Pt was 342 mW/cm², which was higher than those of the CB/PyPBI/Pt (183 mW/cm²) and CB/Pt (115 mW/cm²).

The present study provides useful information for the preparation of an electrocatalyst with a high durability and performance in high temperature PEFCs.

  References

[1]     N. Nakashima et al., Small 2009, 5, 735-740.

[2]     N. Nakashima et al., J. Mater. Chem. 2011, 21, 1187-1190.

[3]     N. Nakashima et al, Scientific Reports, 2013, 3, article no. 1764.

[4]     N. Nakashima et al.,, ChemCatChem, 2014, 6, 567-571.

[5]     N. Nakashima et al, Scientific Reports, 2014, 4, article no.6295.

[6]     N. Nakashima et al., ChemPlusChem, 2014, 79, 400-405.

[7]     Nakashima et al., N., J. Mater. Chem. A 2014, 2, 18875-18880.